Project Summary/ Abstract White-black disparities in the treatment of coronary heart disease (CHD) are due in part to differences in the quality of hospitals used by black and white patients, and studies suggest that non-geographic factors play an important role. Such non-geographic factors likely include differences in the physicians caring for black and white patients with CHD. In support of this hypothesis, research has shown that the care of black patients is concentrated within a small number of physicians, who report lower access to specialists and hospitals, and may be more isolated professionally. In addition, research has shown that black and white patients may be treated differently even when they are cared for by the same physicians or physician referral networks. Whether differences among physicians caring for black and white seniors with CHD contribute to the racial gap in hospital quality remains unknown. The overarching goal of this proposal is to identify and characterize physicians and networks treating black and white seniors with CHD, and to investigate the physician and network factors associated with the racial gap in high quality hospital use using a combination of state of the art social network and econometric data analyses, and surveys directed at physicians caring for black and white patients. The study will include seniors in 35 metro areas with sizable black and white populations and include two cardiac conditions: acute myocardial infarction (AMI), an emergency condition typically requiring transport to the nearest hospital, and coronary artery bypass grafting surgery (CABG), a frequently elective procedure involving specialty referral. Study aims will sequentially construct metro-level networks; identify sub-networks of physicians within the larger metro area that are likely to work together (i.e., referral networks); measure network segregation; measure physician and sub-network characteristics that may be relevant for hospital access and the referral process; survey a sample of physicians within these networks to understand self-reported difficulties with the referral process; estimate regression models to assess the effects of physicians and their measured and self-reported characteristics on the white-black gap in high quality hospital use for CHD; and employ simulations to assess potential policy effects achieved by modifying relevant characteristics. The study will address important, previously unanswered questions about physician referral networks for black and white seniors with CHD in diverse US metro areas. Are networks segregated, and to what degree is network segregation correlated with residential segregation? Are characteristics of physicians and sub-networks used by black and white seniors with CHD (e.g., physician qualifications and the centrality of cardiologists within a sub-network) different and do they affect the use of high quality hospitals? The study will address these important research and policy questions.